This application claims the benefit of Korean Patent Application No. 1999-68074, filed on Dec. 31, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device with electrodes on barrier ribs that is adaptive for widening a viewing angle and improving an aperture ratio.
2. Discussion of the Related Art
Generally, an active matrix liquid crystal display (LCD) of active matrix driving system uses thin film transistors (TFT""s) as switching devices to display a natural moving picture. Since such a liquid crystal display can be made into a smaller-size device than the Brown tube or cathode ray tube (CRT), it is commercially available for a monitor such as a portable television or a lap-top personal computer, etc.
The active matrix LCD displays a picture corresponding to video signals, such as television signals, on a pixel (or picture element) matrix having pixels arranged at each intersection between gate lines and data lines. Each pixel includes a liquid crystal cell for controlling a quantity of transmitted light in accordance with a voltage level of a data signal from a data line. The TFT is installed at an intersection between the gate line and the data line to switch a data signal to be transferred to the liquid crystal cell in response to a scanning signal (i.e., a gate pulse) from the gate line.
Such a liquid crystal display device (LCD) can be largely classified into a twisted nematic (TN) mode, in which a vertical electric field is applied, and an in-plane switching (IPS) mode, in which a horizontal electric field is applied to have a wide viewing angle, depending on a direction of an electric field driving a liquid crystal.
In a TN mode LCD as shown in FIG. 1, a TFT 30 is provided at an intersection between a data line 22 and a gate line 24, and pixel electrodes 20 are arranged in a matrix type at a pixel area between the data line 22 and the gate line 24. As shown in FIG. 2, the TFT 30 is provided on a rear substrate 2. The TFT 30 includes a gate electrode 4 connected to the gate line 24, a source electrode 14 connected to the data line 22, and a drain electrode 16 connected to the pixel electrode 20. A gate insulating film 6 made from SiNX or SiOX, etc. is entirely deposited on the rear substrate 2 in which the gate electrode 4 is patterned. A semiconductor layer 8 made from amorphous silicon (a-Si) and an ohmic contact layer 10 made from a-Si doped with n+ions are sequentially disposed on the gate insulating film 6 in such a manner to cover the gate insulating film 6 on the gate electrode 4. A source electrode 14 and a drain electrode 16 made from a metal are formed on the ohmic contact layer 10. The source and drain electrodes 14 and 16 are patterned in such a manner to be spaced by a predetermined channel width from each other. Subsequently, the ohmic contact layer 10 is etched along a channel defined between the source electrode 14 and the drain electrode 16 to expose the semiconductor layer 8. A protective film 18 made from SiNX or SiOX, etc. is entirely deposited on the rear substrate 2 to cover the TFT 30. The protective film 18 on the drain electrode 16 is etched away to define a contact hole 12. The contact hole 12 and the pixel area are deposited with indium tin oxide (ITO) to connect the pixel electrode 20 to the drain electrode 16.
As, shown in FIG. 3, the rear substrate 2 provided with the TFT array is opposed to a front substrate 62 provided with black matrices 64, color filters 66, and a common electrode 68 of ITO with having a liquid crystal layer 70 therebetween. A gate high pulse is applied to the gate electrode 4 of the TFT, thereby applying an electric field corresponding to a difference voltage between a video data voltage and a common voltage between the pixel electrode 20 and the common electrode 68 opposed vertically to each other during a scanning interval when a channel is defined between the source electrode 14 and the drain electrode 16. The liquid crystals of the liquid crystal layer 70 is driven with the vertical electric field to control a quantity of light input from a back light.
Such a TN mode LCD has a drawback in that, since liquid crystal within the pixel cell has a large difference in refractive index and transmissivity depending on an observed angle, the viewing angle is limited. On the other hand, the IPS mode LCD has an advantage in the viewing angle since liquid crystal within the pixel cell is rotated on a basis of horizontal direction by a horizontal electric field.
In an IPS mode LCD as shown in FIG. 4, a TFT 50 is provided at an intersection between a data line 52 and a gate line 54, and pixel electrodes 48 are arranged in a matrix type at a pixel area between the data line 52 and the gate line 54. As shown in FIG. 5, the TFT 50 is provided on a rear substrate 32. The TFT 50 includes a gate electrode 34 connected to the gate line 54, a source electrode 42 connected to the data line 52, and a drain electrode 44 connected to the pixel electrode 48. The gate electrode 34 and a common electrode 35 are formed on the rear substrate 32 by depositing a metal such as chrome (Cr), etc. and then patterning it. Herein, the common electrode 35 is patterned into a stripe shape within a pixel cell area. A gate insulating film 36 made from SiNX or SiOX, etc. is entirely deposited on the rear substrate 32 provided with the gate electrode 34 and the common electrode 35. A semiconductor layer 38 made from amorphous silicon (a-Si) and an ohmic contact layer 40 made from a-Si doped with n+ions are sequentially disposed on the gate insulating film 36 in such a manner as to cover the gate insulating film 36 on the gate electrode 34. The source electrode 42 and the drain electrode 44 made from a metal are formed on the ohmic contact layer 40. The source and drain electrodes 42 and 44 are patterned in such a manner as to be spaced by a predetermined channel width from each other. Then, ITO is deposited on the drain electrode 44 and the gate insulating film 36 and thereafter patterned to form the pixel electrode 48. Herein, the pixel electrode 48 is connected to the drain electrode 44 and is patterned into a stripe shape in such a manner as to be alternated with the common electrode 35 within the pixel cell area. Subsequently, the ohmic contact layer 40 is etched along a channel defined between the source electrode 42 and the drain electrode 44 to expose the semiconductor layer 38. A protective film 46 made from SiNX or SiOX, etc. is entirely deposited on the rear substrate 32 to cover the TFT 50.
As shown in FIG. 6, the rear substrate 32 provided with the TFT array is opposed to a front substrate 72 provided with black matrices 74 and color filters 76, with a liquid crystal layer 78 therebetween. A gate high pulse is applied to the gate electrode 34 of the TFT, thereby applying an electric field corresponding to a difference voltage between a video data voltage and a common voltage between the pixel electrode 48 and the common electrode 35 opposed horizontally to each other during a scanning interval when a channel is defined between the source electrode 42 and the drain electrode 44. A liquid crystal of the liquid crystal layer 78 is driven with the horizontal electric field to control a quantity of a light input from a back light.
However, the IPS mode LCD has an advantage in that it can achieve a wide viewing angle, but has a disadvantage in that, since the area occupied by the electrodes within the pixel cell area, particularly the common electrode 35 made from a metal is large, it has a low aperture ratio and transmissivity. The IPS mode LCD, as well as the TN mode LCD, has such a limitation in the aperture ratio and transmissivity caused by the electrode area as mentioned above. As the area of the electrode made from ITO or a metal is more enlarged so as to apply a strong enough electric field to drive the liquid crystal, the aperture ratio and the transmissivity become lower. Furthermore, the conventional TN mode and IPS mode LCD""s have a problem in that, since a single pixel cell has to occupy more than a certain area in consideration of an area occupied by the electrodes, it is difficult to improve the resolution.
Accordingly, the present invention is directed to a liquid crystal display device with electrodes on barrier ribs and a method of fabrication thereof that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a liquid crystal display device with electrodes on barrier ribs that is adaptive for widening the viewing angle of the display as well as improving the aperture ratio of the liquid crystal cells.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structures particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a liquid crystal display is provided having first and second electrodes to define pixel cells and a barrier member at the boundary portion of the pixel cells, the first and second electrodes being formed in a vertical structure between the first and second substrates;.
A liquid crystal display device fabricating is also provided which includes: preparing first and second substrates; forming first and second electrodes to define pixel cells, the first and second electrodes being formed with a vertical shape between the first and second substrates; and forming a barrier member at the boundary portion of the pixel cells.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.